A headless metal warrior stomps towards you, shooting. Fortunately, you've been training for a marathon and easily jet off to safety down an alleyway. But wait - - now a metal cheeta-bot is after you, racing faster than your puny legs can go. As the space between you and the galloping beast closes, you round a corner, see a door and dive through. It slams behind you. As you freeze, holding your breath, the robotic cat passes by outside with a wake of metallic echoes.

Relieved, you exhale into the dark. A fatal mistake - - outside, another robot has detected your breath and alerted the enemy to your location ...

Waking up from this nightmare is a way to save yourself, for now, but in fact all three 'terror' bots it featured are based on actual prototypes being developed in California and Boston (though not with directly malicious intentions). Here's an introduction to the motley three.

ATLAS

A headless humanoid is being built by Boston Dynamics. Called Atlas, it has is a heel-to-toe gait. The designers want Atlas to be able to navigate over rough terrain as well as a human can, by resorting to a crawl or turning itself sideways as the situation necessitates. He (she?) also stays upright when pushed and can currently travel at 3.2 miles per hour. Atlas is the improved version of an earlier robo-person, Petman, that was designed to test the Army's chemical weapons suits, while mimicking human movement and physiology. Boston Dynamics recently won DARPA contracts to further develop Atlas and another robot named Cheetah.

CHEETAH

DARPA asked Boston Dynamics to build this robot-cat with a flexible spine, movable head and possibly even a tail. According to this IEEE Spectrum blog, the designers says Cheetah will sprint "faster than any existing legged robot and faster than the fastest human runners." More than a speedy quadruped, Cheetah also has cat-like agility, able to turn corners and zig-zag with ease, as well as making lightning fast starts and stops.

COUGAR 20-H

A mini-surveillance robot more like Johnny 5 than a wildcat, the Cougar 20-H can park itself outside a building and detect activity inside from 65 feet away. The Army-funded rover, built by Orange County, Calif.-based TiaLinx, uses a low-power radar mounted on a tripod that can detect heartbeats and even breathing. As pointed out in Wired'sDanger Room blog, this might actually make the Cougar 20-H well suited for search and rescue missions or for monitoring borders, since it can detect people through walls and underground.